1. Field of the Invention
This invention relates to extruded sheets and, more particularly, to an apparatus for continuously forming a sheet product using a roll stand with cooperating rolls between which material passes during the sheet product formation process.
2. Background Art
Extruded sheets are formed from many different materials, with many different thicknesses, and with different layer constructions. An extruded sheet may be formed by itself or combined with one or more other sheet layers that are concurrently formed, or combined after formation.
In a typical apparatus for extrusion forming sheet products, a roll stand is placed downstream of an extruder assembly with an associated sheet die. Flowable material is delivered through the sheet die to a nip/lamination location between adjacent rolls on the roll stand. The applied material is advanced through a gap between the adjacent rolls defined at the nip/lamination location from where it may be routed between one or more additional roll pairs before it arrives at a downstream accumulation location at which the sheet product may be rolled, stacked, packaged, staged, or otherwise handled or processed.
In one exemplary roll stand, there is a roll that cooperates with two adjacent rolls, with the rolls cooperating to facilitate layer, and ultimately sheet product, formation. The gaps between adjacent rolls must be variable to allow an apparatus to have the flexibility to make layers of different thicknesses and products with potentially different combinations of sheet layers that may have thicknesses varying over a significant range.
Such apparatus may be integrated into a line wherein multiple products with different constitution and/or thickness may be serially produced. Accordingly, it is important that the system operator have the ability to readily and accurately adjust the roll gaps to those appropriate for a particular run.
Given that gap control may be required at a number of different locations, it is also important that the mechanisms for varying the gap be reliable in operation and economically feasible.
Heretofore, gap adjusting mechanisms have varied significantly in terms of their complexity, reliability, and accuracy. At one end of the spectrum, it is known to incorporate relatively simple adjusting mechanisms that are operated using a conventional wrench. The system operator is required to have on hand the requisite tooling/wrench that is moved from location to location on the apparatus to make the necessary adjustments. Since a substantial force may be required to turn the wrench to effect adjustments, operators will commonly use a separate, elongate extender bar that can be grasped and manipulated to provide more leverage.
Additionally, since the gap between adjacent rolls is commonly adjusted through separate mechanisms at the spaced ends of the roll, the operator is often required to make incremental adjustments, going back and forth between the ends until the desired gap is established.
Another drawback with this type of setup is that it is difficult for the operator to determine when the desired gap is actually arrived at. Such a determination may involve using a separate measuring instrument. In the event that the gap is not consistent and of the desired dimension, resulting sheet product may be compromised in terms of quality or could even be unusable, in which event a substantial amount of product may have to be scrapped.
Another known adjusting mechanism incorporates conventional block and tackle components to selectively raise and lower one or more rolls relative to another roll to control gap. While this type of system avoids the requirement that necessary separate tooling be kept on hand, the adjustments made using these types of components may be relatively crude. Again, the difficulty in precisely setting a desired gap and identifying the same without onerous measurements, exists with this design.
As an alternative, it is known to use motorized mechanical devices and/or servohydraulic mechanisms to reposition the rolls to set the gap. As mentioned, these mechanisms can get very complex and expensive and require a power supply.
In one form, a separate actuator is required to be kept on hand to be moved separately to each of the mechanisms that is required to be operated for adjustment of the gap. Since these mechanisms are capable of relatively quickly changing the gap dimensions, the operator may have to change operating directions, one or more times, to compensate for an overrun during the adjustment process.
Still further, these designs require that operators contend with the aforementioned problem of accurately identifying when a desired gap has been established.
With some of the power operated mechanisms, the operating drive will be a separately powered component that must be moved to a number of adjusting mechanisms to individually operate them. In the event that such drives are powered pneumatically or through an electrical lead from a supply, the operator will be required to reposition the drive without entangling the supply lines and the system components.
While the above devices have a number of drawbacks, the industry has continued to use them because there is lacking any substitute that addresses all of the issues relating to cost, convenience, reliability, and accuracy.